1. Field of the Invention
The invention relates to an aqueous emulsion of a water insoluble additive for insulating materials which consist of artifical mineral fibers, and a method of producing such aqueous emulsions and their use for impregnating (oiling) the synthetic mineral fibers. The invention further relates to insulating materials consisting of synthetic mineral fibers which are impregnated by using such aqueous emulsions.
2. Discussion of the Background
In order to improve their handling properties, insulating materials which consist of synthetic mineral fibers are impregnated with additives such as, for example, dust binders, water repellants, smoothing and lubricant agents as well as other additives. Furthermore, synthetic plastics in the form of thermohardenable duromers such as, for example, phenolformaldehyde resins, are added in order to impart a certain form stability to the mineral fibers in the bonded material.
In order to achieve an even distribution of these additives throughout the mineral fibers which are further processed in the form of a fiber strip, it is necessary for the additives to be incorporated at a stage in the manufacturing process at which the fibers can still be impregnated as individual fibers, in other words before the felted fiber web is formed. This stage in the manufacturing process is in the immediate vicinity of the disaggregating units where, by reason of the proximity of molten glass, high temperatures, intensive radiated heat and the latent risk of fire are present.
Therefore, the additives have to fulfill a number of conditions, i.e., they must have low inherent volatility; it must be possible to dilute them with water; it must be possible to work them by spraying, and they must not burn when being processed.
In current processes, these conditions are fulfilled by aqueous emulsions or dispersions of the additives which have the necessary stability and which can be diluted to the desired low working concentration by the addition of water. Insulating materials consisting of mineral fibers and impregnated with these additives are, however, only conditionally suitable for practical use.
The production of an aqueous emulsion of mineral oils which can be used as a dust binding agent, silicones which can be used as water repellants and similar water-insoluble substances is possible only by using emulsifiers. Emulsifiers are surface-active substances of good solubility both in the aqueous and also in the non-aqueous phase. With mineral oil emulsions which are described in the insulants industry as "oiling materials", outstanding values of dust bonding are achieved. The effect can be attributed to two causes:
1. The oiling substance consisting of mineral oil acts as a lubricant during the relative movements of compacting fibers. Thus, friction of glass on glass is reduced and this also reduces the risk of cracking and shattering of glass (glass fibers).
2. Despite all these precautionary measures the dust formed remains clinging to intact fibers and cannot be thrown off into the ambient air. This effect is a consequence of the tackiness of viscous mineral oils. Therefore, impregnation with dust binders is an essential condition for the marketability of an insulating material which consists of synthetic mineral fibers.
It has, however, been demonstrated that insulating materials impregnated with dust binders easily absorb water. For example, if an insulating mat impregnated with dust binders is placed on water, it rapidly swells up and sinks. Water such as, for instance, rain water sprayed onto such a mat is absorbed and soaks the mat. This represents a considerable disadvantage because insulating materials consisting of mineral fibers which have become wetted in use, for example by rain, have to be dried out at considerable expense and there is a latent risk of corrosion from insulating materials which are not fully dried. Furthermore, many emulsifiable mineral oils or other water insoluble additives can be washed out by the action of the clinging emulsifier.
Even silicones which can be used as additives for the water repellant finishing of insulating materials consisting of mineral fibers can as a rule only be processed to produce stable aqueous emulsions by the addition of solvents and if they have very high proportions of emulsifier. Therefore, the hydrophobic action of the silicone is often weakened and sometimes even cancelled out entirely by the hydrophilic influence of the emulsifier, so that the addition of silicone becomes pointless. Only with particular technical complications can the emulsifier--once the emulsion has been applied to mineral fibers--be so altered that it loses its emusifying effect.
Therefore, numerous experiments have been made with a view to avoiding or circumventing the aforesaid disadvantages of processing emuslifier-containing emulsions to produce additives for use with mineral fiber-containing insulating materials. During an attempt to reduce the quantity of added emulsifier, however, the emulsion became too unstable so that the target, i.e. a water repellent finish, could not be achieved.
Furthermore, alkali or ammonium soaps of fatty or resinous acids having been used as emulsifiers. Such substances can be used as effective emulsifiers for highly viscous mineral oils even if the quantity used is only 5% of the mineral oil. The emulsifying effect of soaps can be rendered ineffective by chemical precipitation with lime-milk, e.g. by the simultaneous spraying of soap-containing emulsion and lime-milk. Ammonium soaps can also be destroyed by thermal decomposition as the impregnated product passes through a continuous dryer. It is obvious that the additional spraying of lime-milk or the additional procedural step of heating in a continuous dryer represent a disadvantageous technical and economic complication.
Furthermore, a process is known in which the highly viscous mineral oil used an additive for the insulating materials is so diluted by the addition of an organic solvent that its viscosity becomes similar to that of water. In this form, the mineral oil solution is worked into the synthetic resin solution by means of static mixers and is sprayed jointly with it. The method calls for a high proportion of solvent, of 25 to 40% in relation to the mineral oil used as the dust binder and increases the hydrocarbon emission of the plant to two to three times its original level.